Whenever I've bought a car I've always checked the things that I care about work before I've bought it. If the dealer isn't interested then there's not much you can do. Going to court for that lot on a £4k car would likely cost you more than just to fix them yourself.

Some of those issues should have been picked up by a test drive. If you're not willing/able to do that, then an AA inspection should have picked up all of them, and would put you in a strong negotiating position PRE-sale. If you're not prepared to fork out for that, well... the reputation of used car dealers is well-earned and your mate should expect nothing but a lot of prevarication and obfuscation, and no joy. The only glimmer of light would be if the car was sold with a limited warranty, say 3 months, which a reputable dealer would do as standard.